You already answered your question,he came to avoid END´s Resurrection. He probably has some unfinished business with Zeref and wants to avoid his death.
Zeref, on the other hand, wants END to ressurect because it´s his brother and he wishes for death, so he couldn´t let the book fall into Acnologia´s power.
Acnologia is still a bit of an incognita. He also showed up at Tenrou just because.
No, no, So basically END (natsu) is the strongest being there is and will be, we are so far, when END was supposed to be resurrected in Tartaros arc, Acnologia didn't do one thing, to stop face, like he didn't even destroy one, it was just chance that he ended up there.
However here it gets tricky for me, later when zeref goes to see acnologia, he says that him and his brother, END will give him the battle he so desired, and we see acnologia smyling, eager to face END; yet he came over tartaros in an attempt to stop face and END, because from what I get, END already existed and faced Igneel, defeated him, on top of that Igneel said that even Acnologia fears END, which Acnologia forcely has seen so I just don't get it, is it just bad writing? Am I stupid? Or there is an other reason?
The only Ambiguity I got here is that Natsu is the Stronges of them all, ofc only the 2 strongest mages in the world know about this, And Both Know that END is stronger then them, ( Well In Zeref's case is hope and Trust that he will beat him), So the only thing I got from here, Is that Acnologia fears END, because END will kill him, but at the same time is eager to face him, for i dunno, maybe he hasnt found anyone as strong yet.
So Acnologia wants To Die facing END, Yet he shows up everytime to prevent his resurrection/development, I Find it Odd.